Includes two replacement white membranes for Medela breastpumps. Please note that this is the newer "offset mount" design of the membrane. Older versions of the Medela breastpumps included a "center mount" valve and membrane, and the white membrane plugged directly into the center of the yellow valve (instead of off to the side.) If you have the older "center mount" version of the yellow valve, the newer "offset mount" membranes (sold on this website) will not fit. If you have the "center mount" valve and you need new membranes, you will need to order the newer version of the complete "valve/membrane assembly" to ensure that you have two parts which fit together properly. The "valve/membrane assembly" can be found on the "Medela Spare Parts" page. Please note that we have a $10.00 Minimum for orders.